1. Field of the Invention
This invention relates to mimeographic printing machines, and more particularly to a mimeographic printing machine having a flexible rotary cylindrical printing drum.
2. Description of the Prior Art
For instance, U.S. Pat. No. 4,911,069 and U.S. Pat. No. 5,081,924 have disclosed a mimeographic printing machine which comprises: a flexible rotary cylindrical printing drum made up of a flexible tubular wall having an ink passing structure on which a stencil paper is wound; a lower pusher roller provided in parallel with the flexible rotary cylindrical printing drum with a predetermined space between the lower pusher roller and the drum; and an inside pusher roller provided inside the cylindrical printing drum in such a manner that it is extended in parallel with one of the generating lines of the cylindrical printing drum, the inside pusher roller being movable between a deformation position to push the tubular wall radially outwardly thereby to deform the latter towards the lower pusher roller, and a steady position to release the flexible tubular wall from the deformation, in which machine, with the inside pusher roller at the deformation position, a printing sheet is supplied from a sheet supplying section to the space between the cylindrical printing drum and the lower pusher roller to perform a pressure type mimeographic printing operation, and the printing sheet, after printed, (hereinafter referred to as "a printed sheet", when applicable) is discharged into a sheet discharging section.
In general, in mimeographic printing machines including the above-described machine, printed sheets are stacked on the sheet discharging tray in the sheet discharging section with the print sides at the top. Hence, when, before the ink on a first printing sheet dries, a second printing sheet is laid on the first printing sheet, then an ink transferring phenomenon may occur: that is, the ink of the first printing sheet may partially transfer onto the back of the second printing sheet. That is, the ink set-off may occur.
In order to prevent the ink set-off, the following method has been employed in the art: That is, a blank sheet, namely, an intermediate sheet is laid on the printed sheet, so that the printed sheets are not directly brought into contact with each other.
In providing a number of printed sheets, sometimes it is necessary to group printed sheets every predetermined number of printed sheets. For this purpose, the following sheet supplying device has been proposed in the art. The device automatically inserts a dividing sheet such as a piece of tape between printed sheets on the sheet discharging tray thereby to suitably divide the printed sheets into groups.
In order to automatically supply the intermediate sheet to the sheet discharging tray, it is necessary to provide a high-speed sheet supplying device which is able to supply the intermediate sheets one at a time in synchronization with the sheet discharging operation and at a high speed corresponding to the printing speed of the printing machine so that the intermediate sheets and the printed sheets are alternately delivered to the sheet discharging tray. However, the device is used only for supplying the intermediate sheets, and is considerably expensive. That is, the use of the device is not economical.